The invention relates to a coiled heat exchanger having a plurality of tubes which are wound around a core tube, having a casing which delimits an outer space around the tubes.
Natural gas is continuously liquefied in large quantities in LNG baseload systems. Most of the time, liquefaction of the natural gas is accomplished by heat exchange with a coolant in coiled heat exchangers. However, many other applications of coiled heat exchangers are also known.
In a coiled heat exchanger, several layers of tubes are spirally wound on a core tube. A first medium is piped through the inside of at least one portion of the tubes, and this medium exchanges heat with a second medium flowing in the outer space between the tubes and a surrounding casing. The tubes are merged into several groups on the upper ends of the heat exchanger and fed out of the outer space in a bundled manner.
These types of coiled heat exchangers and their application, for example for liquefaction of natural gas, are described in each of the following publications:                Hausen/Linde, Cryogenic Engineering, 2nd ed., 1985, pages 471-475;        W. Scholz, “Coiled Tube Heat Exchangers,” Linde Reports on Science and Technology, No. 33 (1973), pages 34-39;        W. Bach, “Offshore Natural Gas Liquefaction with Nitrogen Cold—Process Design and Comparison of Coiled Tube and Plate Heat Exchangers,” Linde Reports on Science and Technology, No. 64 (1990), pages 31-37;        W. Förg et al., “A New LNG Baseload Process and Manufacturing of the Main Heat Exchanger,” Linde Reports on Science and Technology, No. 78 (1999), pages 3-11 (English version: W. Förg et al., “A New LNG Baseload Process and Manufacturing of the Main Heat Exchanger,” Linde Reports on Science and Technology, No. 61 (1999), pages 3-11);        DE 1501519 A;        DE 1912341 A;        DE 19517114 A;        DE 19707475 A; and        DE 19848280 A.        
Manufacturing coiled heat exchangers either of aluminum or of steel (stainless steel or special low-temperature steel) is known.
The invention is based on the objective of manufacturing these types of coiled heat exchangers more cost efficiently and/or improving its process engineering properties.
This objective is attained in that a first and a second component of the coiled heat exchanger are composed of different materials.
Until now this was intentionally refrained from for manufacturing-related reasons. On the contrary, attempts were made to use a uniform material for all components of the coiled heat exchanger in order to be able to connect them to one another more easily, particularly by welded joints.
The invention is now diverging from this principle and different materials are being used in the same heat exchanger. As a result, the design of the heat exchanger can be optimized further, for example, with respect to volume, weight, strength and/or cost.
In this connection, the first and the second component can each be formed of the following components:                Core tube, on which the tubes are coiled;        Tubes;        Sections of tubes;        Tube bases (tube collectors);        Casing, which closes the heat exchanger as a pressure vessel to the outside;        Distributor for liquid and/or gas in the outer space of the tubes;        Connecting pieces between two tube layers (spacers);        Support arms to mount the connecting pieces; and        Shroud, which is arranged between the casing and the tubes.        
For example, the casing can be manufactured of steel and the tube bundle(s) can be manufactured of aluminum.
In this case, for example, a first component can be made of aluminum and the second component of steel. Aluminum should be understood here as both pure aluminum as well as every technically useable aluminum alloy, for example with an aluminum content of 50% or more, preferably with an aluminum content of 80% or more. Steel should be understood here as all types of steel, for example austenitic, ferritic, duplex steel, stainless steel and nickel steel.
In a concrete example, the first component can include a group of tubes in a first tube layer and be manufactured of aluminum; a second component can, for example, include another group of tubes of the same or another tube layer and be comprised of steel.
If the first and second components are connected with the same connecting piece, the connecting piece is made preferably of the material of the first component as a basic material and features a plating made of the material of the second component. Thus, the connecting piece can be welded to both the first component as well as to the second component. In a concrete example, aluminum tubes are welded to a tube base of stainless steel that has an aluminum plating.
In addition, the invention relates to the application of this type of heat exchanger for executing an indirect heat exchange between a hydrocarbonaceous stream and at least one heat fluid or cold fluid.
The hydrocarbonaceous stream in this case is formed by natural gas for example.
The hydrocarbonaceous stream is liquefied, cooled, heated and/or vaporized during the indirect heat exchange. The heat exchanger is preferably used for natural gas liquefaction or natural gas vaporization.
Normally, coiled heat exchangers made of aluminum are used for natural gas liquefaction. Alternatively, those made of steel can also be used for natural gas liquefaction.